AU2014253511B1 - A Platform Lift Mechanism for a Boat - Google Patents

Abstract

A platform lift mechanism for a boat includes two spaced apart lift arm assemblies. Each lift arm assembly includes a transom bracket adapted for being fixed to the transom of a boat. A platform lift arm is pivotally connected to the transom bracket. A pivot arm is linked to the platform lift arm at one end, the pivot arm pivotal about a pivot axis to urge the platform lift arm between a raised and a lowered position by pivotal displacement of the pivot arm. A lifting bar extends between the pivot arms of the respective lift arm assemblies, the lifting bar connected to at least one of the pivot arms at a position offset from the pivot axis to pivot the pivot arm by displacement of the lifting bar. A hydraulic ram is linked to the lifting bar to displace the lifting bar.

Description

1 A PLATFORM LIFT MECHANISM FOR A BOAT FIELD [0001] Various exemplary embodiments of a platform lift mechanism, for raising and lowering a swim platform or personal watercraft platform relative to the stern of a boat, are described herein. BACKGROUND [0002] Swim platforms are commonly mounted to the transom of a boat via a hydraulic lift mechanism. The lift mechanism is operable to raise/lower the platform between a raised position and a lowered position. In the raised position the platform is out of the water and usually level with the deck of the boat. In the lowered position the platform is at or below the water level surrounding the boat. [0003] The lift mechanism preferably provides sturdy enough support to the platform so that the platform does not pitch, drop or droop to one side when a user(s) steps onto the platform. Known lift mechanisms have horizontally spaced apart lift arm assemblies pivotally connected to the transom of the boat via brackets to provide the necessary sturdy support to the platform. [0004] Figure 1 of the drawings shows the hydraulic lift apparatus of United States patent US6327992. The lift apparatus has two horizontally spaced lift arms 18. The lift arms 18 are each actuated by a separate hydraulic power cylinder 30. One of the drawbacks of operating each lift arm with a separate hydraulic cylinder is that the stroke of the cylinders need to be synchronized. If the cylinders are out of sync, either because of a delay in actuation of one of the cylinders, actuation at different speeds, or because of sticking, the platform may droop to one side or the whole mechanism may become stuck/jammed or get damaged. The lift apparatus has an intricate hydraulic circuit including a sequence valve, flow divider/combiner and counter balance valves to ensure that the two cylinders 30 operate in unison. [0005] Figure 2 of the drawings shows the transom operating mechanism of Australian Innovation patent AU2010101390. The mechanism uses a single rotary actuator 4 instead of two hydraulic rams to raise/lower the lift arms 7 by rotating a shaft 5. Struts 6 link rotation of the shaft 5 to both lift arms 7. [0006] A problem with such an arrangement is that the torque for lifting the arms 7 is applied directly to the shaft so that is can be transferred to a lifting arm or member fast with the 2 shaft. This is undesirable. Shafts for these forms of mechanism are usually fabricated out of marine grade stainless steel. Such material does not have high resistance to fatigue-based failure. Such failure can occur as a result of repetitive or cyclical torsional stresses applied to the shaft. [0007] A further problem with such an arrangement is that the extent of rotation of the shaft is not readily limited. It is thus necessary to make use of physical stops, such as posts or other stop members. These may be welded or fastened or otherwise operatively arranged on the shaft to stop against a frame or some other fixture to achieve accurate movement limitation. Repetitive striking of the stops or posts can result in failure through fatigue. [0008] Hydraulic rams are mechanically simpler and generally easier to maintain and operate than rotary actuators. Furthermore, extent of movement of hydraulic rams can easily be controlled due to the nature of such movement. However, using two hydraulic rams, one for each lift arm assembly, to raise/lower a swim platform has the disadvantages described above in respect of US6327992. SUMMARY [0009] Various exemplary embodiments of a platform lift mechanism for a boat comprise: two spaced apart lift arm assemblies, each lift arm assembly including: a transom bracket adapted for being fixed to the transom of a boat; a platform lift arm pivotally connected to the transom bracket; and a pivot arm linked to the platform lift arm at one end, the pivot arm pivotal about a pivot axis to urge the platform lift arm between a raised and a lowered position by pivoting displacement of the pivot arm; a lifting bar extending between the pivot arms of the respective lift arm assemblies, the lifting bar connected to at least one of the pivot arms at a position offset from the pivot axis to pivot the pivot arm by displacement of the lifting bar; and a hydraulic ram linked to the lifting bar to displace the lifting bar. [0010] The hydraulic ram may be linked to the lifting bar by a rocker arm that pivots about the same pivot axis as the pivot arm to which the lifting bar is connected. [0011] The lifting bar is preferably connected to the pivot arm at a position offset from the pivot axis. The lifting bar may be connected to the pivot arm at a position intermediate the pivot axis and where the pivot arm is linked to the platform lift arm.

3 [0012] The lifting bar is preferably connected to the pivot arms of both lift arm assemblies. The opposite end regions of the lifting bar may be captured by the respective pivot arms. [0013] The pivot axis about which the pivot arm pivots may be defined by a pin or shaft extending parallel to the lifting bar and which may be retained by the transom bracket. [0014] The hydraulic ram may be pivotally connected to one of the transom brackets. [0015] The platform lift mechanism may include a hydraulically actuated lock mechanism for locking the platform lift arms in the raised position. The lock mechanism may include a hydraulic cylinder pivotally connected to the other of the transom brackets. [0016] The pivot arm may be linked to the platform lift arm via a strut arm which is pivotally connected to the pivot arm at one end and pivotally connected to the platform lift arm at the other end. [0017] The lift arm assemblies preferably include platform brackets pivotally connected to distal ends of the platform lift arms, the platform brackets adapted to be secured to the underside of a platform. The platform lift mechanism may include the platform secured to the lift arm assemblies. BRIEF DESCRIPTION OF THE DRAWINGS [0018] Figure 1 shows a three dimensional view of the hydraulic lift apparatus of United States patent US6327992. [0019] Figure 2 shows a three dimensional view of a transom operating mechanism of Australian Innovation patent AU201010139. [0020] Figure 3 shows a side view of an exemplary embodiment of a platform lift mechanism mounted to a boat. The platform lift mechanism is in a raised condition wherein a platform is raised by the platform lift mechanism to be level with the deck of the boat. [0021] Figure 4 shows a side view of the platform lift mechanism and boat of figure 3, with the platform lift mechanism in a lowered condition wherein the platform is lowered by the platform lift mechanism to below the waterline. [0022] Figure 5 shows a three dimensional view of the platform lift mechanism of figure 3 in the raised condition. [0023] Figure 6 shows a three dimensional view of the platform lift mechanism of figure 5 in the lowered condition.

4 [0024] Figure 7 shows a side view of the platform lift mechanism of figure 5 in the lowered condition. [0025] Figure 8 shows a side view of the platform lift mechanism of figure 5 in the raised condition. [0026] Figure 9 shows a three dimensional sectional view of a port side lift arm assembly of the platform lift mechanism of figure 5. [0027] Figure 10 shows a rendered sectional side view of the port side lift arm assembly of figure 9. [0028] Figure 11 shows a line drawing sectional side view of the port side lift arm assembly of figure 9. [0029] Figure 12 shows a perspective view of an actuating assembly of the platform lift mechanism of figure 5. [0030] Figure 13 shows a perspective view of part of the port side lift arm assembly of figure 9, showing a lifting bar of the platform lift mechanism in a raised position. [0031] Figure 14 shows another perspective view part of the port side lift arm assembly of figure 9, showing the lifting bar of the platform lift mechanism in a lowered position. [0032] Figure 15 shows a three dimensional sectional view of a starboard side lift arm assembly of the platform lift mechanism of figure 5. [0033] Figure 16 shows a sectional side view of the starboard side lift arm assembly of figure 15. [0034] Figures 17A to 17C show three dimensional views of part of the starboard side lift arm assembly of figure 15 and the sequence to lock the platform lift mechanism in the raised condition using a hydraulically actuated lock mechanism. [0035] Figure 18 shows a side view of another exemplary embodiment of a platform lift mechanism mounted to a boat. The platform lift mechanism is in a raised condition wherein a platform is raised by the platform lift mechanism to be level with the deck of the boat. [0036] Figure 19 shows a side view of the platform lift mechanism and boat of figure 18, with the platform lift mechanism in a lowered condition wherein the platform is lowered by the platform lift mechanism to below the waterline.

5 [0037] Figure 20 shows a three dimensional view of the platform lift mechanism of figure 18 in the raised condition. [0038] Figure 21 shows a three dimensional view of the platform lift mechanism of figure 20 in the lowered condition. [0039] Figure 22 shows a side view of the platform lift mechanism of figure 20 in the raised condition. [0040] Figure 23 shows a side view of the platform lift mechanism of figure 20 in the lowered condition. [0041] Figure 24 shows a three dimensional sectional view of a port side lift arm assembly of the platform lift mechanism of figure 20. [0042] Figure 25 shows a three dimensional sectional view of a starboard side lift arm assembly of the platform lift mechanism of figure 20. [0043] Figure 26 shows a stern view of the platform lift mechanism of figure 20, excluding brackets for mounting a swim platform. DESCRIPTION OF THE EMBODIMENTS [0044] In Figures 3 and 4, reference numeral 10 generally indicates an exemplary embodiment of a platform lift mechanism. The platform lift mechanism 10 is mounted to the transom 12 at the stern of a boat 14. The platform lift mechanism 10 is operable to selectively raise or lower a swim platform 16 relative to the stern of the boat 14. The swim platform 16 is also sometimes referred to as a "duckboard" and may be adapted to carry a personal watercraft such as a dinghy or Jet Ski. The platform 16 may include cradles (not shown) for carrying the personal watercraft in a configuration as a personal watercraft platform. [0045] The platform 16 is displaceable between a raised position (shown in figure 3) and a lowered position (shown in figure 4). In the raised position the platform 16 is level with the deck 13 of the boat 14. In the lowered position the platform 16 is at or below the waterline 17. When the swim platform 16 is in the raised position, both the platform 16 and the deck 13 of the boat are in substantially the same plane. When the swim platform 16 is in the lowered position the plane of the swim platform 16 is substantially parallel to the plane of the deck 13 of the boat 14.

6 [0046] Figures 5 to 8 show the platform lift mechanism 10 comprising two spaced apart lift arm assemblies 20, 22, a lifting bar 24, and an actuating assembly 26 (figure 6) including a hydraulic power ram 28. [0047] The lift arm assemblies 20, 22 work in parallel, being connected via the lifting bar 24, to raise and lower the platform 16. [0048] The lift arm assembly 20, hereinafter referred to as the port assembly 20, comprises a transom bracket 30, two parallel platform lift arms 32, two parallel pivot arms 34, two parallel strut arms 36, a parallelogram arm 38, and a platform bracket 39. Figures 9 to 14 show detailed sectional views of the port assembly 20. [0049] The transom bracket 30 has a backplate 40 with holes therein to mount the bracket to the transom of the boat 14 using fasteners such as bolts or the like. The transom bracket 30 is mounted to the port side of the transom. The transom bracket 30 has two parallel inner mounting plates 42 and two parallel outer mounting plates 43 (see figure 12). The mounting plates 42, 43 project orthogonally from the backplate 40. A proximal end of the parallelogram arm 38 is pivotally connected to a lower region of the bracket 30 by being retained between the pair of inner mounting plates 42 by a transverse pin 41. Proximal ends of the lift arms 32 are pivotally connected to the transom bracket 30 by being retained between respective inner and outer mounting plates 42, 43 by transverse pins 33 (figure 11). [0050] The lift arms 32 and parallelogram arm 38 are generally L shaped with an obtuse angle between straight sections of the arms 32, 38. The distal ends of the arms 32, 38 are pivotally connected to the platform bracket 39. [0051] The platform bracket 39 comprises a base plate 44 and parallel skirt plates 45 extending downwardly from sides of the base plate 44 (figures 9 and 10). The arms 32, 38 are pivotally connected to the platform bracket 39 by being retained between the skirt plates 45 by transverse pins 37 (figure 11). The arms 32, 38 and pivot points of the transom bracket 30 and platform bracket 39 are configured so that the base plate 44 of the platform bracket 39 (and hence the platform 16) remains level as the bracket 39 is displaced between the raised and lowered positions. [0052] The pivot arms 34 are pivotally connected to the transom bracket 30 at one end and pivotally connected to the strut arms 36 at the other end. The pivot arms 34 are pivotal about a pivot axis 46 defined by a shaft or pin 48 which connects the pivot arms 34 to the transom bracket 30. The pivot axis 46 is parallel to the lifting bar 24 and offset from the lifting bar 24. The pin 48 is retained between the mounting plates 42, 43 in an orientation 7 extending parallel to the backplate 40. The pivot arms 34 have a bar receiving hole or eye 50 located intermediate the pin 48 and the pin connection to the strut arms 36. A port end of the lifting bar 24 is journaled in the eye 50 to actuate the pivot arms 34 to pivot between a raised position shown in figure 13 and a lowered position shown in figure 14. [0053] The strut arms 36 link the pivot arms 34 to the lift arms 32. The strut arms 32 are pivotally connected to the pivot arms 34 at one end and pivotally connected to the platform lift arms 32 at the other end. Urging the pivot arms 34 to pivot from the lowered position to the raised position raises the lift arms 32 from the lowered position to the raised position via the strut arms 36. [0054] The hydraulic power ram 28 is linked to the pivot arms 34 to pivot the pivot arms 34 by transferring an actuating force to the pivot arms 34 via the lifting bar 24. The lifting bar 24 is actuated between a lowered position and a raised position by the power ram 28. The lifting bar 24 follows an arcuate path between the lowered position and the raised position which is concentric with the pivot axis 46. [0055] The power ram 28 is connected to the lifting bar 24 by a pair of spaced rocker arms 52. The actuating assembly 26 comprises the power ram 28 and the rocker arms 52. [0056] The rocker arms 52 are pivotally connected to the port transom bracket 30. The port transom bracket 30 includes a ram mounting plate 54 (figure 12) adjacent and parallel to the mounting plates 42, 43. The ram mounting plate 54 projects from the back plate 40. The rocker arms 52 are connected to the mounting plates 54, 43 by the pin 48 such that the rocker arms 52 pivot about the same pivot axis 46 as the pivot axis for the pivot arms 34. The rocker arms 52 have a bar receiving hole or eye 56 which is in line with the eyes 50 in the pivot arms 34. The lifting bar 24 extends through, and is captured by, the eyes 50, 56 in the rocker arms 52 and pivot arms 34, respectively. The lifting bar 24 mechanically connects the pivot arms 34 with the rocker arms 52 so that the actuating force exerted on the rocker arms 52 by the power ram 28 is transferred to the pivot arms 34 to urge the pivot arms 34 between the lowered and raised positions. [0057] The power ram 28 comprises a cylinder 60 and a piston rod 62. The ram 28 is of the double-acting type that is well known in the art. The cylinder 60 has a transverse sleeve 64 fixed to a lower end. The power ram 28 is pivotally connected to the port transom bracket 30 by a pin which extends through the sleeve 64 and which is retained between the ram mounting plate 54 and outer plate 43. The distal end of the piston rod 62 has an eye 66. The power ram 28 is pivotally connected to the rocker arms 52 by a pin 29 which extends through the eye 66 and which is retained between the rocker arms 52. The pin 48 about 8 which the rocker arms 52 pivot is located intermediate the bar receiving eyes 56 in the rocker arms 52 and the pin 29 connecting the power ram 28 to the rocker arms 52. [0058] When the piston rod 62 of the power ram 28 is in a retracted condition (as shown in figure 13), the lifting bar 24 is raised. When the piston rod 62 of the power ram 28 is in an extended condition (as shown in figure 13), the lifting bar 24 is lowered. [0059] The lift arm assembly 22, hereinafter referred to as the starboard assembly 22, comprises a transom bracket 70, two parallel platform lift arms 72, two parallel pivot arms 74, two parallel strut arms 76, a parallelogram arm 78, and a platform bracket 79. Figures 15 to 17 show detailed sectional views of the starboard assembly 22. [0060] The transom bracket 70 has a backplate 80 with holes therein to mount the transom bracket 70 to the transom of the boat 14. The transom bracket 70 is mounted to the starboard side of the transom. The transom bracket 70 has two parallel inner mounting plates 82 and two parallel outer mounting plates 83. The mounting plates 82, 83 project orthogonally from the backplate 80. A proximal end of the parallelogram arm 78 is pivotally connected to the transom bracket 70 by being retained between the pair of inner mounting plates 82 by a transverse pin. Proximal ends of the lift arms 72 are pivotally connected to the transom bracket 70 by being retained between respective inner and outer mounting plates 82, 83 by a transverse pin. [0061] The lift arms 72 and parallelogram arm 78 are the same as the lift arms 32 and parallelogram arm 38 of the port assembly 22. The lift arms 72 and parallelogram arm 78 are pivotally connected to the transom bracket 70 in the same manner as the lift arms 32 and parallelogram arm 38 are connected to the transom bracket 30. The platform bracket 79 is the same as the platform bracket 39 of the port assembly 20 and pivotally connected to the arms 72, 78 in the same manner as described for the port assembly 20. [0062] The pivot arms 74 are pivotally connected to the transom bracket 70. The pivot arms 74 are pivotal about a pivot axis 86 defined by a shaft or pin 88 which connects the pivot arms 74 to the transom bracket 70. The pivot axis 86 is in line with the pivot axis 46 of the port assembly 22. The pin 88 is retained between the mounting plates 82, 83 in an orientation extending parallel to the lifting bar 24. The pivot arms 74 have a bar receiving hole or eye 90 intermediate the pin 88 and the pin connection to the strut arms 76. The bar receiving eyes 90 are in line with the eyes 50 in the pivot arms 34 of the port assembly 20. A starboard end of the lifting bar 24 is captured in the eyes 90 to actuate the pivot arms 74 to pivot between a raised position shown in figure 17C and a lowered position shown in figure 17A.

9 [0063] The strut arms 76 link the pivot arms 74 to the lift arms 72. The strut arms 72 are pivotally connected to the pivot arms 74 at one end and pivotally connected to the lift arms 72 at the other end. Urging the pivot arms 74 from the lowered position to the raised position raises the lift arms 72 from the lowered position to the raised position via the strut arms 76. [0064] The hydraulic power ram 28 at the port assembly 20 actuates the pivot arms 74 of the starboard assembly 22 to pivot by raising and lowering of the lifting bar 24. The lifting bar 24 connects the pivot arms 34 of the port assembly 22 to the pivot arms 74 of the starboard assembly 22 so that the pivot arms 34, 74 are raised and lowered in unison. The actuating force exerted on the rocker arms 52 by the power ram 28 is split between the pivot arms 34 and the pivot arms 74 by the lifting bar 24. It is to be noted that this is done without or with relatively little torsional stress being set up in the lifting bar 24. The pivot arms 74 extend in a direction from the pin 88 towards the backplate 80. A lock pin 92 is fixed between the pivot arms 74. Upper ends of the inner mounting plates 82 have notches 94 in which end regions of the lock pin 92 are received when the pivot arms 74 are pivoted to the raised position. The platform lift mechanism 10 includes a hydraulically actuated lock mechanism 100 for locking the pivot arms 74 in the raised position. The lock mechanism 100 is shown in detail in figure 16 with the pivot arms 74 and the lift arms 72 in the raised position. [0065] The lock mechanism 100 comprises a hydraulically actuated lock ram 102 and two hinged catches 104. The catches 104 are pivotally connected to inner mounting plates 82. The catches 104 comprise a hook 106 and a lever 108. The lock ram 102 is connected to the lever 108 to displace the hook 106 between a locked position and an unlocked position. In the locked position the hooks 106 capture the lock pin 92 in the notches 94 by obstructing the path the lock pin 92 must travel to move out of the notches 94. In the unlocked position the hooks 106 are clear of the path of travel of the lock pin 92 such that the lock pin 92 can move into and out of the notches 94. [0066] Figures 17A to 17C show the sequence of locking the platform lift mechanism 10 in a raised condition with the lifting bar 24 raised. Figure 17A shows the platform lift mechanism 10 in a lowered condition with the lifting bar lowered and the lock mechanism 100 unlocked. The lock pin 92 is raised above the notches 94. Figure 17B shows the platform lift mechanism 10 in a raised condition wherein the lift bar 24 is raised such that the lock pin 92 is received in the notches 94. The lock mechanism 100 is still unlocked in the condition of the platform lift mechanism 10 shown in Figure 17B. Figure 17C shows the platform lift mechanism 10 in the locked condition wherein the catches 104 capture the lock pin 92 in the 10 notches 94 with the lift bar 24 is raised. The lift bar 24 cannot be lowered without first actuating the ram 102 to unlock the catches 104 from the lock pin 92. [0067] The catches 104 maintain the raised position of the lifting bar 24, and hence the platform 16. During powered boating, the platform 16 is locked in in the raised position. The motion of the boat over waves cause back pressure in the hydraulic power ram 28 and would require constant fluid pressure or near-perfect seals to maintain the raised position without the lock mechanism 100. [0068] The platform lift mechanism 10 has two spaced apart lift arm assemblies 20, 22 to adequately support the platform 16, but requires only a single hydraulic power ram 28 to simultaneously actuate both lift arm assemblies 20, 22 to raise and lower the platform 16 in unison. The lift bar 24 extending between the two both lift arm assemblies 20, 22 in a configuration wherein it urges the pivot arms 34 of the port assembly 20 and the pivot arm 74 to starboard assembly to pivot in unison when raised or lowered provides for the actuating force of the power ram to be split between the lift arm assemblies 20, 22. [0069] During operation of the mechanism 10, no or little torsional stress is imparted to the lift bar 24. As a result, the lift bar 24 can be fabricated of marine grade stainless steel without the concerns of fatigue fracture that may result from repeated or cyclical torsional stresses. [0070] Figures 18 to 26 show another embodiment of a platform lift mechanism 200. With reference to the preceding drawings, like reference numerals refer to like parts, unless otherwise specified. The use of common reference numerals is intended to be for convenience only and should not be regarded as limiting. Furthermore, where practical, it is envisaged that components of the platform lift mechanism 10 can be interchanged with those of the platform lift mechanism 200. [0071] In Figures 18 to 23, reference numeral 200 generally indicates the platform lift mechanism 200. The platform lift mechanism 200 is mounted to the transom 12 at the stern of the boat 14. The platform lift mechanism 200 is operable to selectively raise or lower the swim platform 16 relative to the stern of the boat 14, the same as platform lift mechanism 10. [0072] The platform 16 is displaceable between a raised position (shown in figures 18, 20 and 22) and a lowered position (shown in figure 19, 21 and 23). In the raised position the platform 16 is level with the deck 13 of the boat 14. In the lowered position the platform 16 is at or below the waterline 17. When the swim platform 16 is in the raised position, both the platform 16 and the deck 13 of the boat are in substantially the same plane. When the 11 swim platform 16 is in the lowered position the plane of the swim platform 16 is substantially parallel to the plane of the deck 13 of the boat 14. [0073] Figures 20 and 21 show the platform lift mechanism 200 comprising two spaced apart lift arm assemblies 220, 222, a lifting bar 224, and an actuating assembly 226 including a hydraulic power ram 228. [0074] The lift arm assemblies 220, 222 work in parallel, being connected via the lifting bar 224, to raise and lower the platform 16. The platform lift mechanism 200 operates in a similar manner to the platform lift mechanism 10. The lift mechanism 200 is configured so that its lifting bar 224 is located relatively lower down along the transom brackets 230 when compared to the location of the lifting bar of the platform lift mechanism 10. [0075] The lift arm assembly 220, hereinafter referred to as the port assembly 220, comprises a transom bracket 230, two parallel platform lift arms 232, two parallel pivot arms 234, two parallel strut arms 236, a parallelogram arm 238, and a platform bracket 239. Figures 22 and 23 show side views of the port assembly 220 in the raised and lowered condition, respectively. [0076] The transom bracket 230 has a backplate 240 with holes therein to mount the bracket 230 to the transom 12 of the boat 14 using fasteners such as bolts or the like. The transom bracket 230 is mounted to the port side of the transom. The transom bracket 230 has two parallel inner mounting plates 242 and two parallel outer mounting plates 243. The mounting plates 242, 243 project orthogonally from the backplate 240. A proximal end of the parallelogram arm 238 is pivotally connected to a lower region of the bracket 230 by being retained between the pair of inner mounting plates 242 by a transverse pin 241. Proximal ends of the lift arms 232 are pivotally connected to the transom bracket 230 by being retained between respective inner and outer mounting plates 242, 243 by transverse pins 233. [0077] The parallelogram arm 238 is generally L shaped with an obtuse angle between straight sections of the arm 238. The distal ends of the arms 232, 238 are pivotally connected to the platform bracket 239. [0078] The platform bracket 239 comprises a base plate 244 and parallel skirt plates 245 extending downwardly from sides of the base plate 244. The arms 232, 238 are pivotally connected to the platform bracket 239 by being connected to the skirt plates 245 by transverse pins 237. The arms 232, 238 and pivot points of the transom bracket 230 and platform bracket 239 are configured so that the base plate 244 of the platform bracket 239 12 (and hence the platform 16) remains level as the bracket 239 is displaced between the raised and lowered positions. [0079] The pivot arms 234 are pivotally connected to the transom bracket 230 at one end and pivotally connected to the strut arms 236 at the other end. The pivot arms 234 are pivotal about a pivot axis 246 defined by a shaft or pin 248 which connects the pivot arms 234 to the transom bracket 230. The pivot axis 246 is parallel to the lifting bar 224 and offset from the lifting bar 224. The pin 248 is retained between the mounting plates 242, 243 in an orientation extending parallel to the backplate 240. The pivot arms 234 have a bar receiving hole or eye 250 located intermediate the pin 248 and the pin connection to the strut arms 236. A port end of the lifting bar 224 is journaled in the eye 250 to actuate the pivot arms 234 to pivot between a raised position shown in figures 18, 20, 22 and a lowered position shown in figures 19, 21, 23. [0080] The strut arms 236 link the pivot arms 234 to the lift arms 232. The strut arms 232 are pivotally connected to the pivot arms 234 at one end and pivotally connected to the platform lift arms 232 at the other end. Urging the pivot arms 234 to pivot from the lowered position to the raised position raises the lift arms 232 from the lowered position to the raised position via the strut arms 236. [0081] The hydraulic power ram 228 is linked to the pivot arms 234 to pivot the pivot arms 234 by transferring an actuating force to the pivot arms 234 via the lifting bar 224 and a pin 225. The lifting bar 224 is actuated between a lowered position and a raised position by the power ram 228. The lifting bar 224 follows an arcuate path between the lowered position and the raised position which is concentric with the pivot axis 246. [0082] The power ram 228 is connected to the lifting bar 224 by a pair of spaced rocker arms 252. The actuating assembly 226 comprises the power ram 228 and the rocker arms 252. [0083] The rocker arms 252 are pivotally connected to the transom bracket 230. The transom bracket 230 includes a pair of ram mounting plates 254. The ram mounting plates 254 project from the back plate 240. The rocker arms 252 are connected to the mounting plates 254 by the pin 248 such that the rocker arms 252 pivot about the same pivot axis 246 as the pivot axis for the pivot arms 234. The rocker arms 252 have a bar receiving hole or eye 256 which is in line with the eyes 250 in the pivot arms 234. The lifting bar 224 extends through, and is captured by, the eyes 250, 256 in the rocker arms 252 and pivot arms 234, respectively. The lifting bar 224 mechanically connects the pivot arms 234 with the rocker arms 252 so that the actuating force exerted on the rocker arms 252 by the power ram 228 13 is transferred to the pivot arms 234 to urge the pivot arms 234 between the lowered and raised positions. [0084] The power ram 228 comprises a cylinder 260 and a piston rod 262. The cylinder 260 has a transverse sleeve 264 fixed to a lower end. The distal end of the piston rod 262 has a transverse eye sleeve 266. The power ram 228 is pivotally connected to the rocker arms 252 by the pin 225 which extends through the sleeve 264 and which is retained between the rocker arms 252. The power ram 228 is pivotally connected to the port transom bracket 230 by a pin 229 which extends through the transverse eye sleeve 266 and which is retained between the ram mounting plates 254. [0085] When the piston rod 262 of the power ram 228 is in a retracted condition (as shown in figure 18, 20, 22), the lifting bar 24 is raised. When the piston rod 262 of the power ram 228 is in an extended condition (as shown in figures 19, 21, 23), the lifting bar 224 is lowered. [0086] The lift arm assembly 222, hereinafter referred to as the starboard assembly 222, is the same as the port assembly 220, but does not include a power ram 228. The power ram 228 may be mounted to either the port assembly 220 or the starboard assembly 222. [0087] The hydraulic power ram 228 at the port assembly 220 actuates the pivot arms 234 of the starboard assembly 222 to pivot by raising and lowering of the lifting bar 224. The lifting bar 224 connects the pivot arms 234 of the port assembly 222 to the pivot arms 234 of the starboard assembly 222 so that the pivot arms 234 of the two assemblies 220, 222 are raised and lowered in unison. [0088] The actuating force exerted by the power ram 228 on the rocker arms 252 of the port assembly 220 is split between the pivot arms 234 of the respective assemblies 220, 222 by the lifting bar 224. It is to be noted that this is done without or with relatively little torsional stress being set up in the lifting bar 224, the same as for the lifting bar 24. During operation of the mechanism 200, no or little torsional stress is imparted to the lift bar 224. As a result, the lift bar 224 can be fabricated of marine grade stainless steel without the concerns of fatigue fracture that may result from repeated or cyclical torsional stresses. [0089] Depending on the configuration of the boat and other factors it may be desirable for the lifting arm to have different orientations. Thus, the inventor envisages that either of the mechanisms 10, 200 can be used, depending on the required configuration. [0090] It is to be understood that the terminology employed above is for the purpose of description and should not be regarded as limiting. The described embodiments are 14 intended to be illustrative of the invention, without limiting the scope thereof. The invention is capable of being practised with various modifications and additions as will readily occur to those skilled in the art. The term "boat" refers to any aquatic vehicle of any size or type including, but not limited to, boats, yachts, pleasure craft, etc. [0091] Various substantially and specifically practical and useful exemplary embodiments of the claimed subject matter are described herein, textually and/or graphically. Variations (e.g., modifications and/or enhancements) of one or more embodiments described herein might become apparent to those of ordinary skill in the art upon reading this application. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the claimed subject matter to be practiced other than as specifically described herein. Accordingly, as permitted by law, the claimed subject matter includes and covers all equivalents of the claimed subject matter and all improvements to the claimed subject matter. Moreover, every combination of the above described elements, activities, and all possible variations thereof are encompassed by the claimed subject matter unless otherwise clearly indicated herein, clearly and specifically disclaimed, or otherwise clearly contradicted by context. [0092] The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to illuminate one or more embodiments and does not pose a limitation on the scope of any claimed subject matter unless otherwise stated. No language in the specification should be construed as indicating any non-claimed subject matter as essential to the practice of the claimed subject matter unless otherwise stated. [0093] Thus, regardless of the content of any portion (e.g., title, field, background, summary, description, abstract, drawing figure, etc.) of this application, unless clearly specified to the contrary, such as via explicit definition, assertion, or argument, or clearly contradicted by context, with respect to any claim, whether of this application and/or any claim of any application claiming priority hereto, and whether originally presented or otherwise: a. there is no requirement for the inclusion of any particular described or illustrated characteristic, function, activity, or element, any particular sequence of activities, or any particular interrelationship of elements; b. no characteristic, function, activity, or element is "essential"; c. any elements can be integrated, segregated, and/or duplicated; d. any activity can be repeated, any activity can be performed by multiple entities, and/or any activity can be performed in multiple jurisdictions; and 15 e. any activity or element can be specifically excluded, the sequence of activities can vary, and/or the interrelationship of elements can vary. [0094] The use of the terms "a", "an", "said", "the", and/or similar referents in the context of describing various embodiments (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms "comprising," "having," "including," and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to,") unless otherwise noted. [0095] Moreover, when any number or range is described herein, unless clearly stated otherwise, that number or range is approximate. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value and each separate sub range defined by such separate values is incorporated into the specification as if it were individually recited herein. For example, if a range of 1 to 10 is described, that range includes all values there between, such as for example, 1.1, 2.5, 3.335, 5, 6.179, 8.9999, etc., and includes all sub ranges there between, such as for example, 1 to 3.65, 2.8 to 8.14, 1.93 to 9, etc. [0096] The use of words that indicate orientation or direction of travel is not to be considered limiting. Thus, words such as "front", "back", "rear", "side", "up", down", "upper", "lower', "top", "bottom", "forwards", "backwards", "towards", "distal", "proximal", "in", "out" and synonyms, antonyms and derivatives thereof have been selected for convenience only, unless the context indicates otherwise. The inventor envisages that various exemplary embodiments of the claimed subject matter can be supplied in any particular orientation and the claimed subject matter is intended to include such orientations. [0097] Accordingly, every portion (e.g., title, field, background, summary, description, abstract, drawing figure, etc.) of this application, other than the claims themselves, is to be regarded as illustrative in nature, and not as restrictive, and the scope of subject matter protected by any patent that issues based on this application is defined only by the claims of that patent.

Claims (11)

1. A platform lift mechanism for a boat, the platform lift mechanism comprising: two spaced apart lift arm assemblies, each lift arm assembly including: a transom bracket adapted for being fixed to the transom of a boat; a platform lift arm pivotally connected to the transom bracket; and a pivot arm linked to the platform lift arm at one end, the pivot arm pivotal about a pivot axis to urge the platform lift arm between a raised and a lowered position by pivotal displacement of the pivot arm; a lifting bar extending between the pivot arms of the respective lift arm assemblies, the lifting bar connected to at least one of the pivot arms at a position offset from the pivot axis to pivot the pivot arm by displacement of the lifting bar; a hydraulic ram to displace the lifting bar; and a rocker arm linking the hydraulic ram to the lifting bar, the rocker arm pivotable about the pivot axis.

2. The platform lift mechanism of claim 1, wherein the lifting bar is connected to the pivot arm at a position offset from the pivot axis

3. The platform lift mechanism of claim 2, wherein the lifting bar is connected to the pivot arm at a position intermediate the pivot axis and where the pivot arm is linked to the platform lift arm.

4. The platform lift mechanism of any one of the preceding claims, wherein the lifting bar is connected to the pivot arms of both lift arm assemblies.

5. The platform lift mechanism of claim 4, wherein opposite end regions of the lifting bar are captured by the respective pivot arms.

6. The platform lift mechanism of claim 1, wherein the pivot axis is defined by a pin or shaft extending parallel to the lifting bar and retained by the transom bracket.

7. The platform lift mechanism of claim 1, wherein one end of the hydraulic ram is pivotally connected to one of the transom brackets.

8. The platform lift mechanism of claim 7, including a hydraulically actuated lock mechanism for locking the platform lift arms in the raised position, the lock mechanism including a hydraulic cylinder pivotally connected to the other of the transom brackets.

9. The platform lift mechanism of claim 1, wherein the pivot arm is linked to the platform lift arm via a strut arm which is pivotally connected to the pivot arm at one end and pivotally connected to the platform lift arm at the other end. 17

10. The platform lift mechanism of claim 1, wherein the lift arm assemblies include platform brackets pivotally connected to distal ends of the platform lift arms, the platform brackets adapted to be secured to the underside of a platform.

11. The platform lift mechanism of claim 10, wherein the platform lift mechanism includes the platform secured to the lift arm assemblies.